Descriptions of the threat have been deliberately vague to avoid leaks. Israeli officials said it could come by air, sea or land.

The targets could include holy sites, schools or hospitals, and could involve coordinated homicide bombings, officials said.

The officials told Fox News the attacks would not necessarily either target or be limited to Israel, but could involve several major Western cities.

Meanwhile, Israeli forces withdrew from the West Bank city of Nablus (search) on Monday after a weeklong operation that resulted in the arrests of dozens of suspected Palestinian militants.

The sweep was one of the largest Israeli military raids in the West Bank in recent months, reflecting Israeli policy to pursue militants in the absence of Palestinian efforts to crack down on violent groups.

The unrelenting violence has frozen efforts to implement the "road map," an internationally backed plan to end three years of bloody violence and move toward a Palestinian state in 2005.

The road map requires the Palestinians to dismantle groups responsible for three years of attacks against Israelis, but Palestinian Prime Minister Ahmed Qureia (search) insists that the way to stop the violence is to negotiate a truce agreement with the militants, including Hamas and Islamic Jihad. Despite Egyptian help, so far he has not succeeded.

In Nablus, residents said the Israeli troops left at dawn, releasing a curfew that confined many of the 150,000 people in the West Bank's largest city to their homes for a week.

The searches at first concentrated on the Balata refugee camp next to the city but widened after a suicide bomber from a nearby village blew himself up at a bus stop near Tel Aviv on Thursday, killing four Israelis.

The Israeli military said its operations in Nablus, which officials call a hotbed of terrorist activity, would continue.

Palestinians demand that Israel stop its raids, charging that innocent people are killed or injured and entire cities and town are subjected to collective punishment in the form of curfews.

The road map also requires Israel to halt construction in Jewish settlements in the West Bank and Gaza Strip and to remove dozens of settlement outposts put up since 2001.

Settlers said Monday that they would resist a government order, signed a day earlier, to remove four outposts. Only one of them is populated — Ginnot Arieh (search), north of Jerusalem, with 25 people. The other three are dummy settlements consisting of a single trailer or temporary structures.

Recently the Israeli Defense Ministry released a list of 43 outposts it said had been removed, but most were of the dummy variety and many were rebuilt after their evacuation.

Oren Brund, the secretary of Ginnot Arieh, said the settlers there would appeal to Israel's Supreme Court and would oppose the evacuation if the court rules against them.

"The Yesha (Settlers') Council will bring thousands of people here and we will not move," Brund told Israel Radio. "There will be a clash ... (but) there will not be a violent confrontation."

Fox News' David Lee Miller and The Associated Press contributed to this report.